The Social and Economic Consequences of Earthquakes

1.3.1 Earthquake consequences and their acceptability

The primary consequence of concern in earthquakes is of course human casualties, i.e. deaths and injuries. According to Steinbrugge (1982), the greatest known number of deaths that have occurred in a single event is 830,000, in the Shaanxi, China, earthquake

Table 1.1 Numbers of deaths caused by a selection of larger twentieth-century earthquakes in various countries (from Steinbrugge, 1982, and NEIC web page)

Date

Location

Magnitude

Deaths

1906 Apr 18

USA, San Francisco

7.8

800

1908 Dec 28

Italy, Messina

7.5

83,000

1923 Sep 1

Japan, Tokyo

7.9

142,807

1927 May 22

China, Nan-Shan

8.3

200,000

1935 May 31

India, Quetta

7.5

30,000-60,000

1939 Jan 24

Chile, Chillan

8.3

28,000

1939 Dec 26

Turkey, Erzincan

7.9

30,000

1949 Aug 5

Ecuador, Pelileo

6.8

6,000

1956 Jun 10-17

Northern Afghanistan

7.7

2,000

1957 Dec 4

Outer Mongolia, Gobi-Altai

8.6

1,200

1960 Feb 29

Morocco, Agadir

5.6

12,000

1962 Sep 1

Northwestern Iran

7.1

12,230

1963 Jul 26

Yugoslavia, Skopje

6.0

1,100

1970 May 31

Northern Peru

7.8

66,794

1972 Dec 23

Nicaragua

6.2

5,000

1974 Dec 28

Pakistan

6.2

5,300

1976 Feb 4

Guatemala

7.5

23,000

1976 Jul 28

China, Tangshan

7.9

245,000-655,000

1976 Aug 17

Philippines, Mindanao

7.9

8,000

1977 Mar 4

Romania, Bucharest

7.2

1,500

1978 Sep 16

Northeast Iran

7.7

25,000

1980 Oct 10

Algeria

7.2

3,000

1985 Sep 19

Mexico

8.1

9,500-30,000

1995 Jan 10

Japan, Kobe

6.9

5,500

1999 Aug 17

Turkey, Koeceli

7.4

17,439

1999 Sep 20

Taiwan, Chi-Chi

7.6

2,400

of January 24, 1556. Thus the number of casualties in any given event varies enormously, depending on the magnitude, location and era of the earthquake. This is illustrated by a selection of 26 of the more important earthquakes of the twentieth century (mostly drawn from Steinbrugge, 1982) as listed here in Table 1.1. These earthquakes occurred in 24 countries in most parts of the world, and range in magnitude from 6.0 to 8.6. Many of the higher casualty counts have been caused by the collapse of buildings made of heavy, weak materials such as unreinforced masonry or earth. Safety in houses in developing countries remains our biggest challenge (Comartin et al., 2004).

In Figure 1.2 are plotted the approximate total numbers of deaths in earthquakes that occurred worldwide in each decade of the twentieth century. This histogram highlights the randomness of the size and location of the earthquake occurrence process, as well as the appalling societal cost, and implied economic cost, of earthquakes. The totals were found by summing the deaths in major earthquakes listed by Steinbrugge (1982) and the NEIC. The totals for each decade do not include deaths from events with less than 1000 casualties, one of the larger omissions being the 1931 Hawke's Bay, New Zealand, earthquake in which about 260 people died (Dowrick and Rhoades, 2005).

Q 300 200 100

1900 10 20 30 40 50 60 70 80 90 2000 20th Century decades

Figure 1.2 Numbers of deaths worldwide caused by large earthquakes in each decade of the twentieth century

The physical consequence of earthquakes for human beings are generally viewed under two headings:

(A) death and injury to human beings;

(B) damage to the built and natural environments.

These physical effects in turn are considered as to their social and economic consequences:

(1) numbers of casualties;

(2) trauma and bereavement;

(3) loss of employment;

(4) loss of employees/skills;

(5) loss of heritage;

(6) material damage cost;

(7) business interruption;

(8) consumption of materials and energy (sustaining resources);

(9) macro-economic impacts (negative and positive).

The above physical and socio-economic consequences should all be taken into account when the acceptable consequences are being decided (i.e. the acceptable earthquake risk).

Both financially and technically, it is possible only to reduce these consequences for strong earthquake shaking. The basic planning aims are to minimize the use of land

1900 10 20 30 40 50 60 70 80 90 2000 20th Century decades

Figure 1.2 Numbers of deaths worldwide caused by large earthquakes in each decade of the twentieth century subject to the worst shaking or ground damage effects, such as fault rupture, landslides or liquefaction. The basic design aims are therefore confined (a) to the reduction of loss of life in any earthquake, either through collapse or through secondary damage such as falling debris or earthquake induced fire, and (b) to the reduction of damage and loss of use of the built environment. (See also Section 6.3.7.)

Obviously, some facilities demand greater earthquake resistance than others, because of their greater social and/or financial significance. It is important to determine in the design brief not only the more obvious intrinsic value of the structure, its contents, and function or any special parts thereof, but also the survival value placed upon it by the owner.

In some countries the greater importance to the community of some types of facility is recognized by regulatory requirements, such as in New Zealand, where various public buildings are designed for higher earthquake forces than other buildings. Some of the most vital facilities to remain functional after destructive earthquakes are dams, hospitals, fire and police stations, government offices, bridges, radio and telephone services, schools, energy sources, or, in short, anything vitally concerned with preventing major loss of life in the first instance and with the operation of emergency services afterwards. In some cases, the owner may be aware of the consequences of damage to his property but may do nothing about it. It is worth noting that, even in earthquake conscious California, it is only since the destruction of three hospitals and some important bridges in the San Fernando earthquake of 1971 that there have been statutory requirements for extra protection of various vital structures.

The consequences of damage to structures housing intrinsically dangerous goods or processes is another category of consideration, and concerns the potential hazards of fire, explosion, toxicity, or pollution represented by installations such as liquid petroleum gas storage facilities or nuclear power or nuclear weapons plants. These types of consequences often become difficult to consider objectively, as strong emotions are provoked by the thought of them. Acknowledging the general public concern about the integrity of nuclear power plants, the authorities in the United Kingdom decided in the 1970s that future plants should be designed against earthquakes, although that country is one of low seismicity and seismic design is not generally required.

Since the 1960s, with the growing awareness of the high seismic risks associated with certain classes of older buildings, programmes for strengthening or replacement of such property have been introduced in various parts of the world, notably for pre-earthquake code buildings of lightly reinforced or unreinforced masonry construction. While the substantial economic consequences of the loss of many such buildings in earthquakes are, of course, apparent, the main motivating force behind these risk-reduction programmes has been social, i.e. the general attempt to reduce loss of life and injuries to people, plus the desire to save buildings or monuments of historical and cultural importance.

While individual owners, designers, and third parties are naturally concerned specifically about the consequences of damage to their own proposed or existing property, the overall effects of a given earthquake are also receiving increasing attention. Government departments, emergency services, and insurance firms all have critical interests in the physical and financial overall effects of large earthquakes on specific areas. In the case of insurance companies, they need to have a good estimate of their likely losses in any single large catastrophe event so that they can arrange sufficient reinsurance if they are over-exposed to seismic risk. Disruption of lifelines such as transport, water, and power systems obviously greatly hampers rescue and rehabilitation programmes.

1.3.2 Economic consequences of earthquakes

Figure 1.3 plots the costs of earthquake material damage worldwide per decade in the twentieth century, where known. The data for the second half of the century comes from Smolka (2000) of Munich Reinsurance. The first half of the century is incomplete, only the material damage costs for the 1906 San Francisco and the 1923 Kanto earthquakes being readily found. As with the twentieth century deaths sequence plotted in Figure 1.2, the costs sequence is seen to be random. However, there is no correlation between the deaths and costs sequences. It appears that if the costs were normalized to a constant population, and if the 1995 Kobe earthquake were not included, there would be no trend to increase to >

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CO 3

ffl CT

Figure 1.3 plots the costs of earthquake material damage worldwide per decade in the twentieth century, where known. The data for the second half of the century comes from Smolka (2000) of Munich Reinsurance. The first half of the century is incomplete, only the material damage costs for the 1906 San Francisco and the 1923 Kanto earthquakes being readily found. As with the twentieth century deaths sequence plotted in Figure 1.2, the costs sequence is seen to be random. However, there is no correlation between the deaths and costs sequences. It appears that if the costs were normalized to a constant population, and if the 1995 Kobe earthquake were not included, there would be no trend to increase

1900 10 20 30 40 50 60 70 80 90 2000

20th Century

1900 10 20 30 40 50 60 70 80 90 2000

20th Century

Figure 1.3 Total costs of earthquake material damage worldwide for each decade of the twentieth century (adapted from Smolka, 2000). Reproduced by permission of the Munich Reinsurance Company with time. However, the global seriousness of earthquake damage losses is undisputed. The economic consequences of earthquakes occur both before and after the event. Those arising before the event include protection provisions such as earthquake resistance of new and existing facilities, insurance premiums, and provision of earthquake emergency services. Insurance companies themselves need to reinsure against large earthquake losses, as mentioned in the previous section.

Post-earthquake economic consequences include:

(1) cost of death and injury;

(3) losses of production and markets;

(4) insurance claims.

The direct cost of damage depends upon the nature of the building or other type of facility, its individual vulnerability, and the strength of shaking or other seismic hazard to which it is subjected.

During the briefing and budgeting stages of a design, the cost of providing earthquake resistance will have to be considered, at least implicitly, and sometimes explicitly, such as for the retrofitting of older structures. The cost will depend upon such things as the type of project, site conditions, the form of the structure, the seismic activity of the region, and statutory design requirements. The capital outlay actually made may in the end be determined by the wealth of the client and his or her attitude to the consequences of earthquakes, and insurance to cover losses.

Unfortunately it is not possible to give simple guides on costs, although it would not be misleading to say that most engineering projects designed to the fairly rigorous Californian or New Zealand regulations would spend a maximum of 10% of the total cost on earthquake provisions, with 5% as an average figure.

The cost of seismic upgrading of older buildings varies from as little as 10% to more than 100% of the replacement cost, depending on the nature of the building, the level of earthquake loadings used, and the amount of non-structural upgrading that is done at the same time as the strengthening. It is sad to record that many fine old buildings have been replaced rather than strengthened, despite it often being much cheaper to strengthen than to replace.

Where the client simply wants the minimum total cost satisfying local regulations, the usual cost-effectiveness studies comparing different forms and materials will apply. For this a knowledge of good earthquake resistant forms will, of course, hasten the determination of an economical design, whatever the material chosen.

In some cases, however, a broader economic study of the cost involved in prevention and cure of earthquake damage may be fruitful. These costs can be estimated on a probabilistic basis and a cost-effectiveness analysis can be made to find the relationship between capital expenditure on earthquake resistance on the one hand, and the cost of repairs and loss of income together with insurance premiums on the other.

For example, Elms and Silvester (1978) found that in communal terms the capital cost savings of neglecting seismic design and detailing would be more than offset by the increased economic losses in earthquakes over a period of time in any part of New Zealand. It is not clear just how low the seismic activity rate needs to be for it to be cheaper in the long term for any given community to omit specific seismic resistance provisions. The availability or not of private sector earthquake insurance in such circumstances would be part of the economic equation.

Hollings (1971) discussed the earthquake economics of several engineering projects. In the case of a 16-storey block of flats with a reinforced concrete ductile frame it was estimated that the cost of incorporating earthquake resistance against collapse and subsequent loss of life was 1.4% of the capital cost of building, while the cost of preventing other earthquake damage was reckoned as a further 5.0%, a total of 6.4%. The costs of insurance for the same building were estimated as 4.5% against deaths and 0.7% against damage, a total of 5.2%. Clearly, a cost-conscious client would be interested in putting up a little more capital against danger from collapse, thus reducing the life insurance premiums, and he or she might well consider offsetting the danger of damage mainly with insurance.

Loss of income due to the building being out of service was not considered in the preceding example. In a hypothetical study of a railway bridge, Hollings showed that up to 18% of the capital cost of the bridge could be spent in preventing the bridge going out of service, before this equalled the cost of complete insurance cover.

In a study by Whitman et al. (1974), an estimate was made of the costs of providing various levels of earthquake resistance for typical concrete apartment buildings of different heights, as illustrated on Figure 1.4. Until further studies of this type have been done, results such as those shown in the figure should be used qualitatively rather than quantitatively.

It is most important that at an early stage the owner should be advised of the relationship between strength and risk so that he can agree to what he is buying. Where stringent earthquake regulations must be followed the question of insurance versus earthquake resistance may not be a design consideration: but it can still be important, for example for designing non-structural partitions to be expendable or if a 'fail-safe' mechanism is proposed for the structure. Where there are loose earthquake regulations or none at all, insurance can be a much more important factor, and the client may wish to spend little on earthquake resistance and more on insurance.

However, in some cases insurance may be more expensive, or unavailable, for facilities of high seismic vulnerability. For example, the latter is often the case for older unrein-forced masonry buildings in some high seismic risk areas of New Zealand, i.e. those built prior to the introduction of that country's earthquake loadings code in 1935. The costs of earthquake damage are discussed further in Chapter 7.

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